Prior to the present invention, various methods were used to make polyimide-siloxanes consisting essentially of chemically combined blocks of polydiorganosiloxane with polyimide. Holub, U.S. Pat. No. 3,325,450 shows the intercondensation of polydiorganosiloxane having terminal diorganoorganoaminosiloxy units with benzophenone dianhydride resulting in the production of polyimide-siloxane. Another procedure involved the intercondensation of polydiorganosiloxane having terminal alkyl amino groups with aromatic bis(ether anhydride) as shown by Heath et al., U.S. Pat. No. 3,847,867. A further example of polyimide-siloxanes is shown by Ryang, U.S. Pat. No. 4,404,350, utilizing a norbornane anhydride terminated organopolysiloxane intercondensed with organic diamine and optionally other aromatic bisanhydride.
The synthesis of 1,3-bis(3,4-dicarboxyphenyl)-1,1,3,3-tetramethyl disiloxane dianhydride is shown by J. R. Pratt et al., Journal of Organic Chemistry, Vol. 38, No. 25, 1973 (4271-4274). A synthesis of the Pratt et al. "siloxane anhydride", and siloxane anhydride of the formula ##STR1## where R and n are as defined below, is shown in my copending application Ser. No. 765,089, filed Aug. 13, 1985, now U.S. Pat. No. 4,709,054 which is assigned to the same assignee as the present invention and incorporated herein by reference. These siloxane anhydrides can be made by effecting reaction between a functionalized disilane and an aromatic acyl halide in the presence of an effective amount of a transition metal catalyst and thereafter hydrolyzing the resulting halosilyl aromatic anhydride.
The present invention is based on my discovery that siloxane anhydride of Formula (1), aromatic anhydride terminated organopolysiloxane of the formula ##STR2## or equilibrated mixtures thereof, can be used to make polyimide-siloxane by intercondensation with organic diamine having the formula EQU NH.sub.2 R.sup.2 NH.sub.2, (3)
where R is a C.sub.(1-14) monovalent hydrocarbon radical or a C.sub.(1-14) monovalent hydrocarbon radical substituted with the same or different radicals neutral during intercondensation, R.sup.1 is a C.sub.(6-14) trivalent aromatic organic radical, R.sup.2 is a C.sub.(2-20) divalent organic radical, and n is an integer equal to 1 to about 2000 inclusive. In Formula (2), n is preferably 5 to about 2000 inclusive.
The siloxane anhydrides of Formulas (1) and (2) and mixtures thereof also can be equilibrated with cyclopolydiorganosiloxane of the formula ##STR3## where R is as previously defined and P is an integer equal to 3 to 8 inclusive, or siloxane anhydride of Formula (1) can be equilibrated with a mixture of cyclopolydiorganosiloxane of Formula (4) and triorganosiloxane chain stopper, such as hexamethyldisiloxane. Additional chain stopper such as tetramethyldiphenyldisiloxane, 1,3-divinyltetramethyldisiloxane, or mixtures thereof also can be used.